Method of generating a drive signal for a vibratory sensor

Abstract

A method ( 600 ) of generating a drive signal for a vibratory sensor ( 5 ) is provided. The method ( 600 ) includes vibrating a vibratory element ( 104, 510 ) configured to provide a vibration signal, receiving the vibration signal from the vibratory element ( 104, 510 ) with a receiver circuit ( 134 ), generating a drive signal that vibrates the vibratory element ( 104, 510 ) with a driver circuit ( 138 ) coupled to the receiver circuit ( 134 ) and the vibratory element ( 104, 510 ), and comparing a phase of the generated drive signal with a phase of the vibration signal.

We claim: 
     
       1. A method ( 600 ) of generating a drive signal for a vibratory sensor ( 5 ), the method comprising:
 vibrating a vibratory element ( 104 ,  510 ) configured to provide a vibration signal; 
 receiving the vibration signal from the vibratory element ( 104 ,  510 ) with a receiver circuit ( 134 ); 
 generating the drive signal that vibrates the vibratory element ( 104 ,  510 ) with a driver circuit ( 138 ) coupled to the receiver circuit ( 134 ) and the vibratory element ( 104 ,  510 ); 
 comparing a phase of the generated drive signal with a phase of the vibration signal; and 
 generating a command frequency ω from the comparison of the phase of the generated drive signal and the phase of the vibration signal; 
 wherein the drive signal is generated at the command frequency ω by an open-loop drive ( 147 ) in the driver circuit ( 138 ). 
 
     
     
       2. The method ( 600 ) of  claim 1 , wherein the comparing the phase of the generated drive signal with the phase of the vibration signal comprises comparing a sampled generated drive signal with a sampled vibration signal. 
     
     
       3. The method ( 600 ) of  claim 2 , further comprising removing at least one frequency component from the at least one of the sampled generated drive signal and the sampled vibration signal. 
     
     
       4. The method ( 600 ) of  claim 2 , wherein the comparing the sampled generated drive signal with the sampled vibration signal comprises performing a correlation of the sampled generated drive signal and the sampled vibration signal. 
     
     
       5. The method ( 600 ) of  claim 2 , wherein the comparing the sampled generated drive signal with the sampled vibration signal comprises:
 conjugating one of the sampled generated drive signal and the sampled vibration signal; and 
 multiplying the conjugated one of the sampled generated drive signal and the sampled vibration signal with the non-conjugated one of the sampled generated drive signal and the sampled vibration signal. 
 
     
     
       6. The method ( 600 ) of  claim 1 , wherein the comparing the phase of the generated drive signal with the phase of the vibration signal comprises:
 determining a measured phase difference ϕ m  between the phase of the generated drive signal and the phase of the vibration signal; and 
 comparing the measured phase difference ϕ m  with a target phase difference ϕ t  to determine if the measured phase difference ϕ m  is at the target phase difference ϕ t . 
 
     
     
       7. The method ( 600 ) of  claim 6 , further comprising measuring a density of a fluid when the measured phase difference ϕ m  is at the target phase difference ϕ t . 
     
     
       8. The method ( 600 ) of  claim 1 , further comprising:
 providing the command frequency ω to a signal generator ( 147   c ); and 
 generating the drive signal at the command frequency ω with the signal generator ( 147   c ). 
 
     
     
       9. The method ( 600 ) of  claim 8 , wherein the generating the drive signal at the command frequency ω with the signal generator ( 147   c ) comprises:
 forming a synthesized drive signal with a drive synthesizer ( 544 ); and 
 converting the synthesized drive signal to the generated drive signal with a digital to analog converter ( 534 ). 
 
     
     
       10. A vibratory sensor ( 5 ), comprising:
 a vibratory element ( 104 ,  510 ) configured to provide a vibration signal; 
 a receiver circuit ( 134 ) that receives the vibration signal from the vibratory element ( 104 ); and 
 a driver circuit ( 138 ) coupled to the receiver circuit ( 134 ) and the vibratory element ( 104 ), the driver circuit ( 138 ) configured to:
 generate a drive signal that vibrates the vibratory element ( 104 ,  510 ); 
 compare a phase of the generated drive signal with a phase of the vibration signal; and 
 determine a command frequency co from the comparison of the phase of the generated drive signal and the phase of the vibration signal; 
 
 wherein the drive signal is generated at the command frequency ω by an open-loop drive ( 147 ) in the driver circuit ( 138 ). 
 
     
     
       11. The vibratory sensor ( 5 ) of  claim 10 , the driver circuit ( 138 ) being configured to compare a sampled generated drive signal with a sampled vibration signal. 
     
     
       12. The vibratory sensor ( 5 ) of  claim 11 , wherein the driver circuit ( 138 ) is further configured to remove at least one frequency component from at least one of the sampled generated drive signal and the sampled vibration signal. 
     
     
       13. The vibratory sensor ( 5 ) of  claim 11 , wherein the driver circuit ( 138 ) is further configured to perform a correlation of the sampled generated drive signal and the sampled vibration signal. 
     
     
       14. The vibratory sensor ( 5 ) of  claim 11 , wherein the driver circuit ( 138 ) is further configured to:
 conjugate one of the sampled generated drive signal and the sampled vibration signal; and 
 multiplies the conjugated one of the sampled generated drive signal and the sampled vibration signal with the non-conjugated one of the sampled generated drive signal and the sampled vibration signal. 
 
     
     
       15. The vibratory sensor ( 5 ) of  claim 10 , wherein the driver circuit ( 138 ) is comprised of a phase detector ( 147   b ,  542 ) configured to:
 determine a measured phase difference ϕ m  between the phase of the generated drive signal and the phase of the vibration signal; and 
 compare the measured phase difference ϕ m  with a target phase difference ϕ t  to determine if the measured phase difference ϕ m  is at the target phase difference ϕ t . 
 
     
     
       16. The vibratory sensor ( 5 ) of  claim 15 , wherein the driver circuit ( 138 ) is further configured to measure the density of the fluid when the measured phase difference ϕ m  is at the target phase difference ϕ t . 
     
     
       17. The vibratory sensor ( 5 ) of  claim 10 , wherein the driver circuit ( 138 ) is comprised of:
 a phase detector ( 147   b ,  542 ) and a signal generator ( 147   c ) wherein: 
 the phase detector ( 147   b ) is configured to determine the command frequency ω from the comparison of the phase of the generated drive signal and the phase of the vibration signal and provides the command frequency ω to a signal generator ( 147   c ); and 
 the signal generator ( 147   c ) configured to generate the drive signal at the command frequency ω. 
 
     
     
       18. The vibratory sensor ( 5 ) of  claim 17 , wherein the signal generator ( 147   c ) comprises:
 a drive synthesizer ( 544 ) configured to form a synthesized drive signal; and 
 a digital to analog converter ( 534 ) configured to convert the synthesized drive signal to the generated drive signal.